A continuous process for the preparation of diols

Abstract

The application provides a continuous preparation method of dihydric alcohol, and belongs to the technical field of dihydric alcohol hydrogenation; the preparation method comprises the following steps: preparing a Cu / Zn / SiO2 catalyst, activating the catalyst, and feeding; the method for preparing the Cu / Zn / SiO2 catalyst is as follows: polyaniline is added into a Zn(NO3)2 solution, after soaking for 4-6 hours, filtration is carried out, the filter cake is added into a copper nitrate solution, ammonia water and alkaline silica sol are added dropwise in sequence, then sealing and stirring are carried out for 3-4 hours to obtain a mixed solution, after heating and evaporation until the pH value is 6-7, filtration, washing and drying are carried out, and the Cu / Zn / SiO2 catalyst is obtained by calcining at 400-500 DEG C for 4-5 hours; the continuous preparation method of dihydric alcohol has a catalyst service life of 38-41 days, a conversion rate of 99.3-99.5%, a selectivity of 97.5-98.3%, and the prepared 1,6-hexanediol has a purity of 99.1-99.5%.

Description

Technical Field

[0001] This invention belongs to the field of diol hydrogenation technology, specifically relating to a continuous preparation method for diols. Background Technology

[0002] Diols are organic compounds containing two hydroxyl groups in their molecules. Among them, C4 to C6 aliphatic diols are the main raw materials for synthesizing polyester polyols. For example, polyester polyols produced from 1,6-hexanediol can give products excellent mechanical properties and hydrolysis resistance. Polyurethane and polyester resin products produced from 1,5-pentanediol have excellent low-temperature resistance and outstanding comprehensive performance.

[0003] The mainstream production methods for 1,6-hexanediol and 1,5-pentanediol are the dimethyl adipate hydrogenation method and the dimethyl glutate hydrogenation method, respectively. Taking 1,6-hexanediol as an example, the dimethyl adipate hydrogenation method is currently the absolute mainstream route for the industrial production of 1,6-hexanediol worldwide. Its core is to first esterify adipic acid with methanol to obtain dimethyl adipate, and then reduce it to 1,6-hexanediol through fixed-bed catalytic hydrogenation. Finally, the high-end product is obtained through distillation purification. The type and quality of the catalyst play a crucial role in the entire reaction process.

[0004] In the hydrogenation system of dimethyl adipate, noble metal catalysts (Ag, Au, Pt) and non-noble metal catalysts (Cu, Ni, Co) are the two main types of catalysts explored by researchers. Among them, Cu-based catalysts are favored due to their low cost and high activity. Compared with Ni and Co, Cu-based catalysts can selectively hydrogenate C=O without reacting with C+C, and have greater selectivity for the target product 1,6-hexanediol. The main catalytic principle is that the main active component of Cu-based catalysts is Cu. 0 and Cu + Cu + It can polarize dimethyl adipate molecules to directly affect the reaction rate of ester hydrogenation, while Cu 0 This can provide adsorption sites for H2.

[0005] However, the Taman temperature of Cu is only 134℃, while the hydrogenation reaction temperature of dimethyl adipate is 180-220℃. At this temperature, Cu is prone to sintering and growth, and active sites are rapidly lost. Using a support to improve the dispersion of Cu and inhibit high-temperature sintering is the current mainstream modification route.

[0006] Patent CN118056616A discloses a method for preparing a copper-based catalyst, the copper-based catalyst, and its application. The method uses SiO2 to support Cu, which improves the dispersion of Cu. However, there is an upper limit to the amount of Cu that SiO2 can support. The upper limit is low. After the upper limit is exceeded, the anchoring points on the support surface become saturated, and local agglomeration is very likely to occur, forming large-diameter Cu particles. This leads to a simultaneous decrease in catalyst activity and selectivity. Secondly, SiO2 mainly acts as a physical adsorption agent for Cu. Under long-term high-temperature conditions, Cu atoms are very likely to break through weak interactions and migrate and agglomerate, that is, Cu is sintered, which in turn reduces activity and lifetime.

[0007] To further improve the loading and adsorption of Cu pairs by SiO2, adding catalyst promoters (such as transition metals La, Ce, Zr, Zn, etc.) is a common approach. On the one hand, since transition metals have multiple valence states, their corresponding oxides also have excellent redox properties. On the other hand, transition metal oxides can form Cu-OM composite structures with Cu components through strong interactions, further improving the adsorption of Cu and thus enhancing the catalyst's anti-sintering effect.

[0008] Wang Yingbin. Controllable preparation of Cu / SiO2 catalyst structure and study on hydrogenation of dimethyl adipate to 1,6-hexanediol [D]. Shenyang University of Chemical Technology, 2021. This paper proposes that introducing a second metal into the structure of Cu / SiO2 catalysts can enhance the interaction between active sites and the support by synergistically regulating the electronic state of copper, thus improving the activity and stability of the catalyst. The effects of Zn and Ce as promoters on Cu / SiO2 catalysts were studied. The results showed that the addition of Zn or Ce enhanced the interaction between the metal and the support, i.e., the adsorption of Cu was strengthened under the combined action of SiO2 and the promoters. However, the paper also pointed out that the addition of promoters hindered the formation of layered copper silicate (the final form of the support), resulting in slight defects in the support. At the defects, the loading of Cu decreased, the interaction force decreased, leading to local Cu loss and sintering. Although this method improves the overall catalyst effect, the improvement is not ideal due to the presence of defects. Summary of the Invention

[0009] To address the problems existing in the prior art, this invention provides a continuous preparation method for diols, achieving the following objectives: providing a Cu / Zn / SiO2 catalyst that avoids the additive Zn hindering the formation of layered copper silicate during the preparation process, resulting in a catalyst with good stability, high conversion rate and selectivity, and high purity of the obtained 1,6-hexanediol.

[0010] To solve the above technical problems, the technical solution adopted by the present invention is as follows: A continuous preparation method for diols, comprising: 1. Preparation of Cu / Zn / SiO2 catalyst Polyaniline was added to a Zn(NO3)2 solution and soaked for 4–6 hours. After filtration, the filter cake was washed with deionized water and then added to a copper nitrate solution. Subsequently, ammonia and alkaline silica sol were added dropwise at a rate of 120–140 r / min. After the addition was completed, the mixture was stirred in a sealed container at a rate of 40–60 r / min for 3–4 hours to obtain a mixed solution. The mixed solution was heated at 70–80 °C to evaporate to a pH of 6–7. The resulting solid product and washing liquid were then filtered and washed. The solid product was then dried at 100–120 °C for 10–12 hours and calcined at 400–500 °C for 4–5 hours to obtain a Cu / Zn / SiO2 catalyst. The particle size of the polyaniline is 1–3 μm; The Zn(NO3)2 solution has a mass fraction of 4-5%; The mass ratio of polyaniline to Zn(NO3)2 solution is 0.8–1.2:50–60; The copper nitrate solution has a mass fraction of 7-9%; The mass fraction of the ammonia solution is 10-15%. The alkaline silica sol is prepared by diluting sodium silicate solution to a SiO2 content of 10-20%, adjusting the pH value to 2-4 with dilute hydrochloric acid, aging at a temperature of 2-8 hours, adjusting the pH value to 9-10 with ammonia water, and obtaining alkaline silica sol by ultrafiltration, concentration, and desalination. The mass ratio of the filter cake, copper nitrate solution, ammonia water, and alkaline silica sol is 0.8–1.2:50–60:6–7:11–13; The polyaniline was tested and found to have an initial mass ratio of 8 to 10:1 to the mass ratio of solids (mainly polyaniline) in the washing liquid, meaning that most of the polyaniline was inserted into the catalyst structure.

[0011] 2. Catalyst activation The Cu / Zn / SiO2 catalyst was loaded into a fixed-bed reactor. After purging with nitrogen for 30–50 min, a nitrogen-hydrogen mixture with a hydrogen concentration of 10–15% was introduced. The temperature was increased to 110–120 °C at a rate of 10–15 °C / h and held for 1.2–1.5 h. Then, the temperature was increased to 180–200 °C at a rate of 5–10 °C / h and held for 2–3 h. Finally, the current temperature was maintained for 1–1.5 h to slowly replace all the nitrogen-hydrogen mixture with hydrogen. The temperature was then reduced to 180–200 °C and held for 2–3 h. Activation was then complete, and the reactor was ready to feed.

[0012] 3. Feeding Dimethyl adipate was mixed with methanol and then simultaneously introduced into a static mixer with hydrogen gas. After thorough mixing, the mixture was heated to 180–200°C via a heat exchanger and then introduced into a fixed-bed reactor. After the reaction was completed, the mixture was cooled to 110–120°C and purified in three stages via a distillation column to obtain 1,6-hexanediol. The mass ratio of dimethyl adipate, methanol, and hydrogen is 17-18:13-15:8-12; The fixed-bed reactor has a reaction temperature of 180–200℃, a pressure of 8–12 MPa, and a liquid hourly space velocity of 0.4–0.6 h⁻¹. -1 ; The three-stage purification process involves distillation column 1, which operates at atmospheric pressure, with a top temperature of 64–66°C, a bottom temperature of 110–120°C, and a reflux ratio of 1.5–2.0. The top product is methanol, and the bottom product is crude 1,6-hexanediol after methanol removal, which is then fed into distillation column 2. The distillation column 2 operates at a pressure of 5–10 kPa, a top temperature of 120–130°C, a bottom temperature of 150–160°C, and a reflux ratio of 3–5. The top product is light component impurities, and the bottom product is crude 1,6-hexanediol after light component removal, which is then fed into distillation column 3. The distillation column 3 operates at a pressure of 1–3 kPa, a top temperature of 160–170°C, a bottom temperature of 190–200°C, a reflux ratio of 5–8, and produces 1,6-hexanediol as the top product and heavy component impurities as the bottom product.

[0013] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. In the preparation of Cu / Zn / SiO2 catalyst, the ammonia stripping method is used. The principle is as follows: copper salt (copper nitrate solution) is first reacted with ammonia water to form a stable deep blue copper ammonia complex ion [Cu(NH3)4]. 2+ Then, it is thoroughly mixed with an alkaline silica sol rich in silanol groups on its surface. Under alkaline conditions, copper ammonia complex ions react with Si-O on the silica sol surface. - Ion exchange occurs, causing copper species to be uniformly anchored on the silica surface. Subsequently, the system is heated to evaporate ammonia gas, and the pH of the solution gradually decreases. The copper-ammonia complex decomposes and precipitates uniformly in situ, reacting with SiO2 to form a layered copper silicate structure. Furthermore, because polyaniline (which adsorbs Zn(NO3)2 internally) is added to the copper nitrate solution, polyaniline is inserted into the structure while forming the layered copper silicate structure. After drying and calcination, a highly dispersed Cu / Zn / SiO2 catalyst is obtained. After catalyst activation, the strong interaction between Zn and Cu and the isolation and confinement of SiO2 jointly enhance the adsorption of Cu, hindering the spontaneous movement of Cu atoms, thus improving the anti-sintering effect and effectively improving the stability and service life of the copper catalyst.

[0014] 2. Polyaniline can effectively isolate Zn(NO3)2, preventing it from hindering the formation of layered copper silicate. The resulting catalyst has a well-structured structure and a high copper loading. Furthermore, polyaniline has good electrical conductivity and is electronically active. After absorbing energy, high-energy electrons transition to the polyaniline surface and react with Cu. 2+ Its function is to effectively reduce Cu through the reduction of electrons. 2+ Converted to Cu + Secondly, it effectively inhibits Cu 0 and Cu + To Cu 2+ The transformation involves polyaniline having the effect of inhibiting the deactivation of Cu / Zn / SiO2 catalysts and improving their catalytic activity.

[0015] 3. The continuous preparation method of diol of the present invention has good catalyst stability, a lifespan of 38 to 41 days, high activity, a conversion rate of 99.3 to 99.5%, a selectivity of 97.5 to 98.3%, and the purity of the obtained 1,6-hexanediol is 99.1 to 99.5%. Detailed Implementation

[0016] Example 1 1. Preparation of Cu / Zn / SiO2 catalyst Polyaniline was added to a Zn(NO3)2 solution and soaked for 5 hours. After filtration, the filter cake was washed with deionized water and then added to a copper nitrate solution. Subsequently, ammonia and alkaline silica sol were added dropwise at a rate of 130 r / min. After the addition was completed, the mixture was stirred in a sealed container at a rate of 50 r / min for 3.5 hours to obtain a mixed solution. The mixed solution was heated at 75°C to evaporate to a pH of 6.5. The resulting solid product and washing liquid were then filtered and washed. The solid product was then dried at 110°C for 11 hours and calcined at 450°C for 4.5 hours to obtain a Cu / Zn / SiO2 catalyst. The polyaniline has a particle size of 2 μm; The Zn(NO3)2 solution has a mass fraction of 4.5%. The mass ratio of the polyaniline to the Zn(NO3)2 solution is 1:55; The copper nitrate solution has a mass fraction of 8%; The mass fraction of the ammonia solution is 13%. The alkaline silica sol is prepared by diluting sodium silicate solution to a SiO2 content of 15%, adjusting the pH value to 3 with dilute hydrochloric acid, aging at a constant temperature for 5 hours, adjusting the pH value to 9.5 with ammonia water, and then obtaining alkaline silica sol through ultrafiltration, concentration, and desalination. The mass ratio of the filter cake, copper nitrate solution, ammonia, and alkaline silica sol is 1:55:6.5:12. The polyaniline was tested and found to have an initial mass ratio of 9:1 to the mass ratio of solids (mainly polyaniline) in the washing liquid, meaning that most of the polyaniline was inserted into the catalyst structure.

[0017] 2. Catalyst activation The Cu / Zn / SiO2 catalyst was loaded into a fixed-bed reactor. After purging with nitrogen for 40 min, a nitrogen-hydrogen mixture with a hydrogen concentration of 13% was introduced. The temperature was increased to 115℃ at a rate of 12℃ / h and held for 1.4 h. Then, the temperature was increased to 190℃ at a rate of 7℃ / h and held for 2.5 h. Finally, the current temperature was maintained for 1.3 h to slowly replace all the nitrogen-hydrogen mixture with hydrogen. The temperature was then reduced to 190℃ and held for 2.5 h. Activation was then complete, and the reactor was ready to feed.

[0018] 3. Feeding Dimethyl adipate was mixed with methanol and then simultaneously introduced into a static mixer with hydrogen gas. After thorough mixing, the mixture was heated to 190°C via a heat exchanger and then introduced into a fixed-bed reactor. After the reaction was completed, the mixture was cooled to 115°C and purified through a three-stage distillation column to obtain 1,6-hexanediol. The mass ratio of dimethyl adipate, methanol, and hydrogen is 17.5:14:10; The fixed-bed reactor has a reaction temperature of 190℃, a pressure of 10MPa, and a liquid hourly space velocity of 0.5h. -1 ; The three-stage purification process involves distillation column 1, which operates at atmospheric pressure, with a top temperature of 65°C, a bottom temperature of 115°C, and a reflux ratio of 1.7. The top product is methanol, and the bottom product is crude 1,6-hexanediol after methanol removal, which is then fed into distillation column 2. The distillation column 2 operates at a pressure of 8 kPa, a top temperature of 125°C, a bottom temperature of 155°C, and a reflux ratio of 4. The top product is light component impurities, and the bottom product is crude 1,6-hexanediol after light component removal, which is then fed into distillation column 3. The distillation column 3 operates at a pressure of 2 kPa, a top temperature of 165°C, a bottom temperature of 195°C, a reflux ratio of 7, and produces 1,6-hexanediol as the top product and heavy component impurities as the bottom product.

[0019] Example 2 1. Preparation of Cu / Zn / SiO2 catalyst Polyaniline was added to Zn(NO3)2 solution and soaked for 4 hours. After filtration, the filter cake was washed with deionized water and then added to copper nitrate solution. Subsequently, ammonia and alkaline silica sol were added dropwise at a rate of 120 r / min. After the addition was completed, the mixture was stirred in a sealed container at a rate of 40 r / min for 3 hours to obtain a mixed solution. The mixed solution was heated at 70°C to evaporate to pH 6. The resulting solid product and washing liquid were then filtered and washed. The solid product was then dried at 100°C for 10 hours and calcined at 400°C for 4 hours to obtain the Cu / Zn / SiO2 catalyst. The polyaniline has a particle size of 1 μm; The Zn(NO3)2 solution has a mass fraction of 4%; The mass ratio of the polyaniline to the Zn(NO3)2 solution is 0.8:50; The copper nitrate solution has a mass fraction of 7%; The mass fraction of the ammonia solution is 10%. The alkaline silica sol is prepared by diluting sodium silicate solution to a SiO2 content of 10%, adjusting the pH value to 2 with dilute hydrochloric acid, aging at a constant temperature for 2 hours, adjusting the pH value to 9 with ammonia water, and then obtaining alkaline silica sol through ultrafiltration, concentration, and desalination. The mass ratio of the filter cake, copper nitrate solution, ammonia, and alkaline silica sol is 0.8:50:6:11. The polyaniline was tested and found to have an initial mass ratio of 8:1 to the mass ratio of solids (mainly polyaniline) in the washing liquid, meaning that most of the polyaniline was inserted into the catalyst structure.

[0020] 2. Catalyst activation The Cu / Zn / SiO2 catalyst was loaded into a fixed-bed reactor. After purging with nitrogen for 30 minutes, a nitrogen-hydrogen mixture with a hydrogen concentration of 10% was introduced. The temperature was increased to 110°C at a rate of 10°C / h and held for 1.2 hours. Then, the temperature was increased to 180°C at a rate of 5°C / h and held for 2 hours. Finally, the current temperature was maintained for 1 hour to slowly replace all the nitrogen-hydrogen mixture with hydrogen. The temperature was then reduced to 180°C and held for 2 hours. Activation was then complete, and the reactor was ready to feed.

[0021] 3. Feeding Dimethyl adipate was mixed with methanol and then simultaneously introduced into a static mixer with hydrogen gas. After thorough mixing, the mixture was heated to 180°C via a heat exchanger and then introduced into a fixed-bed reactor. After the reaction was completed, the mixture was cooled to 110°C and purified through a three-stage distillation column to obtain 1,6-hexanediol. The mass ratio of dimethyl adipate, methanol, and hydrogen is 17:13:8; The fixed-bed reactor has a reaction temperature of 180℃, a pressure of 8MPa, and a liquid hourly space velocity of 0.4h.-1 ; The three-stage purification process involves distillation column 1, which operates at atmospheric pressure, with a top temperature of 64°C, a bottom temperature of 110°C, and a reflux ratio of 1.5. The top product is methanol, and the bottom product is crude 1,6-hexanediol after methanol removal, which is then fed into distillation column 2. The distillation column 2 operates at a pressure of 5 kPa, a top temperature of 120°C, a bottom temperature of 150°C, and a reflux ratio of 3. The top product is light component impurities, and the bottom product is crude 1,6-hexanediol after light component removal, which is then fed into distillation column 3. The distillation column 3 operates at a pressure of 1 kPa, a top temperature of 160°C, a bottom temperature of 190°C, a reflux ratio of 5, and produces 1,6-hexanediol as the top product and heavy component impurities as the bottom product.

[0022] Example 3 1. Preparation of Cu / Zn / SiO2 catalyst Polyaniline was added to Zn(NO3)2 solution and soaked for 6 hours. After filtration, the filter cake was washed with deionized water and then added to copper nitrate solution. Subsequently, ammonia and alkaline silica sol were added dropwise at a rate of 140 r / min. After the addition was completed, the mixture was stirred in a sealed container at a rate of 60 r / min for 4 hours to obtain a mixed solution. The mixed solution was heated to 80 °C and evaporated to pH 7. The resulting solid product and washing liquid were then filtered and washed. The solid product was then dried at 120 °C for 12 hours and calcined at 500 °C for 5 hours to obtain the Cu / Zn / SiO2 catalyst. The polyaniline has a particle size of 3 μm; The Zn(NO3)2 solution has a mass fraction of 5%; The mass ratio of the polyaniline to the Zn(NO3)2 solution is 1.2:60; The copper nitrate solution has a mass fraction of 9%; The mass fraction of the ammonia solution is 15%. The alkaline silica sol is prepared by diluting sodium silicate solution to a SiO2 content of 20%, adjusting the pH value to 4 with dilute hydrochloric acid, aging at a constant temperature for 8 hours, adjusting the pH value to 10 with ammonia water, and then obtaining alkaline silica sol through ultrafiltration, concentration, and desalination. The mass ratio of the filter cake, copper nitrate solution, ammonia water, and alkaline silica sol is 1.2:60:7:13. The polyaniline was tested and found to have an initial mass ratio of 10:1 to the mass ratio of solids (mainly polyaniline) in the washing liquid, meaning that most of the polyaniline was inserted into the catalyst structure.

[0023] 2. Catalyst activation The Cu / Zn / SiO2 catalyst was loaded into a fixed-bed reactor. After purging with nitrogen for 50 min, a nitrogen-hydrogen mixture with a hydrogen concentration of 15% was introduced. The temperature was increased to 120°C at a rate of 15°C / h and held for 1.5 h. Then, the temperature was increased to 200°C at a rate of 10°C / h and held for 3 h. Finally, the current temperature was maintained for 1.5 h to slowly replace all the nitrogen-hydrogen mixture with hydrogen. The temperature was then reduced to 200°C and held for 3 h. Activation was then complete, and the reactor was ready to feed.

[0024] 3. Feeding Dimethyl adipate was mixed with methanol and then simultaneously introduced into a static mixer with hydrogen gas. After thorough mixing, the mixture was heated to 200°C via a heat exchanger and then introduced into a fixed-bed reactor. After the reaction was completed, the mixture was cooled to 120°C and purified through a three-stage distillation column to obtain 1,6-hexanediol. The mass ratio of dimethyl adipate, methanol, and hydrogen is 18:15:12. The fixed-bed reactor operates at a reaction temperature of 200°C, a pressure of 12 MPa, and a liquid hourly space velocity of 0.6 h⁻¹. -1 ; The three-stage purification process involves distillation column 1, which operates at atmospheric pressure, with a top temperature of 66°C, a bottom temperature of 120°C, and a reflux ratio of 2.0. The top product is methanol, and the bottom product is crude 1,6-hexanediol after methanol removal, which is then fed into distillation column 2. The distillation column 2 operates at a pressure of 10 kPa, a top temperature of 130°C, a bottom temperature of 160°C, and a reflux ratio of 5. The top product is light component impurities, and the bottom product is crude 1,6-hexanediol after light component removal, which is then fed into distillation column 3. The distillation column 3 operates at a pressure of 3 kPa, a top temperature of 170°C, a bottom temperature of 200°C, a reflux ratio of 8, and produces 1,6-hexanediol as the top product and heavy component impurities as the bottom product.

[0025] Comparative Example 1 Based on Example 1, step 1 is modified as follows, while the remaining steps are the same; 1. Preparation of Cu / Zn / SiO2 catalyst After Zn(NO3)2 solution and copper nitrate solution were mixed evenly, ammonia water and alkaline silica sol were added dropwise at a rate of 130 r / min. After the addition was completed, the mixture was stirred in a sealed container at a rate of 50 r / min for 3.5 h to obtain a mixed solution. The mixed solution was heated and evaporated at 75 °C to a pH of 6.5. The resulting solid product was filtered and washed, then dried at 110 °C for 11 h and calcined at 450 °C for 4.5 h to obtain a Cu / Zn / SiO2 catalyst. The Zn(NO3)2 solution has a mass fraction of 4.5%. The copper nitrate solution has a mass fraction of 8%; The mass fraction of the ammonia solution is 13%. The alkaline silica sol is prepared by diluting sodium silicate solution to a SiO2 content of 15%, adjusting the pH value to 3 with dilute hydrochloric acid, aging at a constant temperature for 5 hours, adjusting the pH value to 9.5 with ammonia water, and then obtaining alkaline silica sol through ultrafiltration, concentration, and desalination. The mass ratio of the Zn(NO3)2 solution, copper nitrate solution, ammonia water, and alkaline silica sol is 6:55:6.5:12.

[0026] Test case 1. The 1,6-hexanediol prepared in Examples 1-3 and Comparative Example 1 were subjected to the following data tests, and the test results are shown in Table 1: Table 1

[0027] As shown in Table 1, Comparative Example 1 did not use polyaniline to load Zn(NO3)2, which hindered the formation of layered copper silicate during the preparation of Cu / Zn / SiO2 catalyst. This resulted in the loss of some copper species, increased copper particle size, and reduced SiO2 strength, which in turn reduced catalyst lifetime, reduced loading, and consequently reduced conversion and selectivity.

Claims

1. A continuous preparation method for diols, characterized in that: The preparation method includes preparing a Cu / Zn / SiO2 catalyst, catalyst activation, and feeding. The feeding method is as follows: dimethyl adipate is mixed with methanol and then simultaneously introduced into a static mixer with hydrogen and thoroughly mixed. After being heated to 180-200°C by a heat exchanger, it is then introduced into a fixed-bed reactor. After the reaction is completed, the temperature is lowered to 110-120°C, and after three-stage purification in a distillation column, 1,6-hexanediol is obtained. The method for preparing the Cu / Zn / SiO2 catalyst is as follows: Polyaniline is added to a Zn(NO3)2 solution and soaked for 4-6 hours. After filtration, the filter cake is washed with deionized water and then added to a copper nitrate solution. Subsequently, ammonia and alkaline silica sol are added dropwise at a rate of 120-140 r / min. After the addition is complete, the mixture is stirred in a sealed container at a rate of 40-60 r / min for 3-4 hours to obtain a mixed solution. The mixed solution is heated at 70-80℃ to evaporate to a pH of 6-7. The resulting solid product and washing liquid are then filtered and washed. The solid product is then dried at 100-120℃ for 10-12 hours and calcined at 400-500℃ for 4-5 hours to obtain the Cu / Zn / SiO2 catalyst. The Cu / Zn / SiO2 catalyst was loaded into a fixed-bed reactor.

2. The continuous preparation method of a diol according to claim 1, characterized in that: In the method for preparing Cu / Zn / SiO2 catalyst, the particle size of polyaniline is 1-3 μm; The mass fraction of the Zn(NO3)2 solution is 4-5%; The mass ratio of polyaniline to Zn(NO3)2 solution is 0.8–1.2:50–60; The mass fraction of copper nitrate solution is 7-9%; The mass fraction of ammonia in the solution is 10-15%. The alkaline silica sol is prepared by diluting sodium silicate solution to a SiO2 content of 10-20%, adjusting the pH value to 2-4 with dilute hydrochloric acid, aging at a temperature of 2-8 hours, adjusting the pH value to 9-10 with ammonia water, and then obtaining alkaline silica sol through ultrafiltration, concentration, and desalination. The mass ratio of filter cake, copper nitrate solution, ammonia water, and alkaline silica sol is 0.8–1.2:50–60:6–7:11–13.

3. The continuous preparation method of a diol according to claim 1, characterized in that: The catalyst activation method is as follows: Cu / Zn / SiO2 catalyst is loaded into a fixed-bed reactor, nitrogen is introduced for purging for 30-50 minutes, then a nitrogen-hydrogen mixture with a hydrogen concentration of 10-15% is introduced, the temperature is increased to 110-120℃ at a rate of 10-15℃ / h, and held at this temperature for 1.2-1.5 hours. Then the temperature is increased to 180-200℃ at a rate of 5-10℃ / h, and held at this temperature for 2-3 hours. Finally, the current temperature is maintained for 1-1.5 hours to slowly replace all the nitrogen-hydrogen mixture with hydrogen, the temperature is then reduced to 180-200℃ and held at this temperature for 2-3 hours. Activation is then complete, and the reactor is ready to feed.

4. The continuous preparation method of a diol according to claim 1, characterized in that: In the feeding method, the mass ratio of dimethyl adipate, methanol, and hydrogen is 17-18:13-15:8-12. A fixed-bed reactor was used, with a reaction temperature of 180–200℃, a pressure of 8–12 MPa, and a liquid hourly space velocity of 0.4–0.6 h⁻¹. -1 .

5. The continuous preparation method of a diol according to claim 1, characterized in that: In the feeding method, the three-stage purification process involves distillation column 1, which operates at atmospheric pressure, with a top temperature of 64–66°C, a bottom temperature of 110–120°C, and a reflux ratio of 1.5–2.

0. The top product is methanol, and the bottom product is crude 1,6-hexanediol after methanol removal, which is then fed into distillation column 2. Distillation column 2 operates at a pressure of 5–10 kPa, with a top temperature of 120–130°C and a bottom temperature of 150–160°C. The reflux ratio is 3–5. The top product is light component impurities, and the bottom product is crude 1,6-hexanediol after light component removal. It is then fed into distillation column 3. Distillation column 3 operates at a pressure of 1–3 kPa, with a top temperature of 160–170°C, a bottom temperature of 190–200°C, a reflux ratio of 5–8, and produces 1,6-hexanediol as the top product and heavy component impurities as the bottom product.

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